Why does the autumnal equinox change from year to year?

Arab Weather - The autumnal equinox of the year (2022) occurred on September 23, and in 2021 it was on September 22, meaning that the equinox does not necessarily occur on the same day each year, as the autumnal equinox occurs in the northern half between September 22/23, and it may coincide with In some years it's September 21 or 24, so why isn't there a fixed date for the autumnal equinox each year? But it changes from year to year!

What is the reason for changing the date of the autumnal equinox?

The equinox is the exact moment when the sun is directly above the equator and the Earth's axis is not tilted toward or away from the sun. At this moment, the northern and southern hemispheres receive an equal amount of sunlight, and the length of the day and night are approximately equal throughout the world - hence the term "equinox".

In most years, this happens either on September 22 or 23. However, the autumnal equinox can occur on September 21 or 24.

This date changes because the length of a calendar year (365 days) does not equal the time it takes the Earth to revolve around the sun (365.25 days), and this extra quarter of a day (6 hours) accumulates each year, so a "leap day" (February 29) is added to The calendar, every four years, causing the dates of the equinoxes and solstices to change from year to year.

The direction of the planet towards the sun is constantly changing, because the tilt of the Earth's axis is not fixed, but rather fluctuates every few years, and thus the dates of the beginning of the astronomical seasons change from year to year.

The last time the autumnal equinox occurred was on September 21, more than a thousand years ago, and the last equinox was on September 24, 1931, according to timeanddate.com. The equinox is expected to occur on September 21, twice in the next century, first in 2092 and then in 2096. The next equinox will be on September 24 in the year 2303.

See also: Facts about the autumnal equinox 2022 and the change in weather features with the onset of autumn